Tubular mesh cathode for high-power electronic tubes



June l0, 1969 J. M. sARRols TUBULAR MESH CATHODE FOR HIGH-POWER ELECTRONIC TUBES l ofz .Sheet Filed July 5, 1966 new raf:

s, W4 ff f5 /n N, MW I@ June 10, 1969 J. M. sARRols 3,449,616

TUBULAR MESH CATHODE FOR HIGH-POWER ELECTRONIC TUBES Filed July s, 1966 sheet 2 of 2 United States Patent O Inf. Cl. lion 19/08 U.S. Cl. 313-341 8 Claims ABSTRACT OF THE DISCLSURE A cathode for high-power electronic tubes includes a plurality of tubular wire mesh portions, the axial length of each portion being shorter than their respective diameters. The ends of the mesh portions are xed to the edge of circular plates so that sagging and other undesired deformations of the cathode when the tube is hot are substantially eliminated.

The present invention relates to improvements in lamentary or directly heated cathodes, and in particular to cathodes of this type intended to operate in high-power electronic tubes.

Filamentary cathodes for high-power electronic tubes often have the appearance of a tubular cage constituted by a mesh of tungsten wires stretched between two circular plates, the ends of these wires being soldered or Welded to the periphery of the plates. According to an advantageous construction, the wires are distributed in two layers wihch are respectively inclined in opposite directions with respect to a generating line of the cylinder so as to form a lmesh (mesh cathode). This type of cathode has practically no radial deformation when hot, if certain conditions are complied with, and in particular if the angle of inclination of the helical wires is greater than 60 with respect to a generating line, and if one takes the precaution of soldering or welding the wires together at the points where they intersect.

However, in very high power tubes, the height of the cathode is relatively large and, at operational temperatures, the tungsten Wires sag under their own weight so that the base of the cathode becomes enlarged while its upper part narrows. This leads to a considerable change in the cathode-grid space and the result is a change also of the characteristics of the tube and consequently disturbances in the operation of the equipment, such as an amplifier or oscillator utilizing this tube. Moreover, Where the cathode approaches towards the control grid, the grid becomes locally overloaded and this may lead to its destruction.

It is an object of the present invention to provide a cathode construction having such characteristics that the geometry thereof remains substantially stable when hot.

The present invention provides a llamentary cathode for electronic tubes in which the emissive part is constituted by a tubular structure made of a mesh of metallic wires attached to the edge of circular plates, said mesh resulting from helical Winding of the wires in opposite direction of two layers of wires. According to the present invention, the emissive part of the cathode comprises at least two portions of metal wire mesh tube in alignment on a common axis, and the ends of each portion are respectively fixed to the edge of two circular plates which are spaced axially by a distance smaller than their diameter.

It has been observed that at their operational temperature, mesh cathodes can retain a cylindrical shape without presenting any notable deformation, on the condition that their height is less than their diameter. According to a feature of the present invention, the cathode is constituted of a plurality of superposed portions of metal mesh tube, having their ends attached to rigid plates. Under these conditions, each portion acts as an elementary emissive part, and it does not undergo any harmful notable deformation under the etfect of heat, because its height is smaller than its diameter. EIn order that deformation is as small as possible, it is recommended to observe the abovementioned directions and in particular to construct the metal mesh tube with layers of wires which are inclined respectively in opposite directions at more than 60 with respect to a generatix of the tube.

The cathode according to the present invention may take various forms. For example, the e-missive part of the cathode may be constituted by an uninterrupted tubular body composed of a mesh of metallic wires. In this case, the emissive part of the cathode is iixed on the one hand to plates arranged at its ends (and plates) and on the other hand to plates arranged in its tubular space (intermediate plates) at axial distances which are shorter than the diameter of the tube. Each intermediate plate is then a common support for two adjacent portions of the cathode. In another form, the emissive part of the cathode may comprise a plurality of sections of metal wire mesh tube. In this case, two adjacent sections may be connected to a common intermediate plate but they may also be respectively connected to two separate intermediate plates. According to an advantageous embodiment, the two separate intermediate plates are in the form of flat-bottomed dishes and they are connected by their dished portions. In this case, the edges of the dishes are slightly separated and delimit a zone which, during the opeartion of the cathode, remains relatively cold and supplies no electronic emission. In an electronic tube containing such a cathode, it is then possible to reinforce the control by rigid rings ensuring the cylindrical shape of this electrode which is fragile. These rings are placed opposite the intermediate plates and consequently they are not directly subjected to the electron bombardment of the cathode, nor to its thermal radiation. They are relatively cold and ensure, by conduc-tion, the cooling of the grid wires.

The elementary portions of the cathode may be fed in series or in parallel. To this end, the plates are supported by current input conductors which may be constituted either by rigid rods, or by a system of coaxial conductors. When -a conductor traverses a plate which is at a potential which is different from that of the conductor, it is xed to this plate by means of an insulating member.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

FIGURES 1, 2 and 3 are sectional views illustrating respectively three different embodiments of a cathode according to the present invention.

FIGURE 1 shows a cathode according to the present invention comprising an emissive element 1, formed Jby three portions such as 30 connected in series by the structural elements. The emissive element 1 which is tubular in shape and has the appearance of a mesh, is produced by two thoriated tungsten wires wound helically in opposite directions, with an inclination greater than 60 on either side o'f a generatrix (t-wo layers of thoriated tungsten Wires). lAt its ends, the emission element 1 is closed by circular end plates 2, 3, made of molybdenum. Two other intermediate circular plates 4, 5, also made of molybdenum, are located in the tubular space of the emissive element 1, so that the distance between any adjacent two plates is smaller than their diameter. Moreover, the plates 2 to S are connected to support rods arranged in the longitudinal direction of the cathode. In FIGURE l, the support rods are divided up into a rst group of two rods 6, and a second group of two rods 7. A terminal part (not shown in the figure) of the two groups of rods is rigidly fixed to the electrode supporting stem of an electron tube (not shown). By their other terminal part, the rods 6 are xed to the plate 2 at the upper end (in the gure) of the cathode, whilst the rods 7 are Xed to the lower plate 3. Starting from their points of attachment to the upper plate 2, the rods 6 successively pass through the intermediate plates 4, and the lower plate 3. The rods 6 are electrically insulated from these plates by discs 8, made of ceramic material, sealed to the plates. In addition, the intermediate plates 4, 5 are rigidly attached to the rods `6 `by means of nuts 9 gripping the insulating discs 8.

Thus a cathode is obtained which comprises three portions, delimited by the four circular plates 2 to 5. According to the invention, each portion is of a .height smaller than its diameter, and this ensures that the wires constituting the emissive element of the cathode will not undergo, when they are hot, any substantial sagging action, which is harmful to the good retention of a cylindrical form of the cathode. In this embodiment, the three portions of cathode are fed in series by means of rods `6 and 7 serving as current input conductors.

FIGURE 2 shows another embodiment according to which two cathode portions 31 and 32 are separated by a double plate 10- constituted by twoelementary plates 10a and 10b, each in the form of a `flat-bottomed dish, which are joined, for example riveted, as shown, at their dished portions so that the periphery of the double plate 10 comprises two separated rims. The emissive part of the cathode is formed by two tubular sections 11 and 12 of metal wire mesh. The ends of the tubular meshed portion 11 are attached to the periphery of an upper plate 13 and to the upper rim of the plate 10, whilst the ends of the section 12 are attached to the periphery of a lower plate 14 and to the lower rim of the plate 10.

The plates 10, 13, 14 are supported by coaxial tubular columns 17, 18, 19 respectively, serving both as support means and as current input conductors. At their lower end (in the figure) the coaxial columns 17, 18, 19 are connected to the electrode supporting stem of an electronic tube having a metal-ceramic envelope comprising connecting rings 20, 21, 22, 2.3 sealed to ceramic spacer cylinders such as 27. It may be seen that in this embodiment, the two cathode portions 11 and 12 have their ends connected to current input conductors; consequently, it is possible to feed them either in series or in parallel as desired.

At its upper part, the tubular column 17 supporting the double plate 10 is pierced by perforations 24. These perforations permit more rapid cooling by radiation of the central column 18, after the cathode is turned off. The tungsten wires, having a very low thermal inertia, are very quick to cool, and may be subjected to stretching if the columns 17 and 18 were still at high temperature and thus heat expanded. The perforations 24 vmade in the column 17 permit the thermal radiation of the column 18 to be effected towards the outside. An annular insulator 26 is placed between the columns 17 and 18 above the perforations 24 to limit the deformations which could result from transverse shocks which are produced in the course of handling of the electronic tube containing such a cathode.

In order to show a particular advantage of the cathode utilizing the double intermediate plate 10 of FIGURE 2, the cathode is shown surrounded by a control grid 16. A zone 15 between the peripheral rims of the plate 10 remains relatively cold during the opeartion of the cathode and consequently is not subject to electronic emission. At the level of the zone 15, it is thus possible to reinforce the control grid 16 with the aid of a rigid ring 25. This ring is not directly subjected to electron bombardment or by the thermal radiation of the cathode. It thus also remains relatively cold and ensures a cooling of the grid w1res.

FIGURE 3 illustrates a modication of the cathode shown in FIGURE 2. In these two ligures, identical components are designated by the same references. In FIG- URE 3, the plates 10, 13, 14 are supported by two coaxial tubular columns 26, 27 whose lower ends (not shown in the figure) are connected to an electrode supporting stem of an electronic tube (not shown). The upper end of the internal column 26 is connected to the plate 10, whilst the upper end of the external column 27 is connected to the plate 14. Moreover, the plate 13 is rigidly connected to the plate 14 by means of three rods such as 28, fixed at three points which are angularly equidistant about the plates 13 and 14, and traversing the plate 10 through insulating holes 29. In the embodiment shown in FIGURE 3, the two portions of cathode 11 and 12 are connected in parallel by the support structure, the columns 26, 27 constituting the two conductors necessary for supplying the current.

What I claim is:

1. A cathode for electronic tubes comprising:

a generally tubular structure consisting of a plurality of separate tubular metal wire mesh portions mounted in axial alignment, the axial lengths of each of said tubular mesh portions being shorter than their respective diameters;

lirst and second substantially circular end plates attached to the remote ends of said generally tubular structure, respectively; and

at leastA one substantially circular intermediate plate located in axial alignment with said tubular mesh portions and mounted between said rst land second end plates, said intermediate plate being attached to an intermediate end of at least one of said tubular mesh portions forming said structure.

2. Cathode according to claim 1 comprising a plurality of substantially circular intermediate plates and wherein the adjacent ends of two adjacent tubular mesh portions are connected to separate adjacent plates.

3. Cathode according to claim 1 further comprising a plurality of tubular columns supporting the plates, said tubular columns forming a system of coaxial conductors.

4. Cathode according to claim 3 further comprising a base coaxial with said system of coaxial conductors to support said system of coaxial conductors, said base forming the stem of a metal-ceramic tube.

v 5. Cathode according to claim `4, wherein the separate plates are in the form of flat-bottomed dishes and are joined by their dished portions.

6. Cathode according to claim 1, including rigid rods supporting said plates and constituting current conductors.

7. Cathode according to claim 6, wherein at least one of said rods passes through a plate and including insulator means interposed between said rod and said plate to permit 3,449,616 5 operation at a potential which is different from that of the rod.

-8. Cathode according to claim 5, in combination with a grid in an electron tube, wherein the control grid sur- 736,542 rounds the cathode and comprises, in the zone of the 5 987,461 plates, at least one rigid ring to improve the cooling of 1229220 the grid wires.

References Cited UNITED STATES PATENTS 2,456,649 12/1948 Rouse S13- 337x 10 2,882,436 4/1959 Dorgelo 313-348 X 3,172,002 3/1965 Johnson et al 313--341 6 FOREIGN PATENTS 4/1946 Australia.

5/ 1951 Great Britain. 9/ 1955 Great Britain. 3/ 1965 Great Britain. 3 1960 France.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

U.S. Cl. X.R. 

